An established connection between a base station and a mobile station in a digital mobile system of today usually utilizes one time slot per frame for transmitting speech information from the base station to the mobile station on a first radio channel, and one time slot per frame for transmitting speech information in the opposite direction on a second radio channel. A specific time slot on the first and the second radio channel is therefore allocated to the mobile station. Thus, the maximum number of simultaneous connections in this known system is the same as the number of time slots per frame on the radio channels.
It is already known to increase the capacity on the radio channels so that the number of possible simultaneous connections can exceed the number of time slots. The idea is based on reusing time slots when the users are not speaking. The method has been used for trans ocean cables under names like TASI before. In these cases the technique has been used for achieving double capacity. Unfortunately, this goal, together with the way it was implemented has not given the TASI-systems good reputation because they did not work in a good way.
It is known that frames on radio channels, apart from time slots, also contains guard spaces. For example there can be a guard space between each time slot. The guard spaces are used for avoiding the information transmitted from the mobile stations, completely or partially, overlapping each other in the receiver of the base station.